The field of the invention relates to ignition systems for internal combustion engines.
Conventional ignition systems of the Kettering type include a secondary coil having an output terminal, or tower, coupled to the center tower of a distributor. As the distributor rotor rotates in response to camshaft rotation, the secondary coil is coupled across each spark plug. The primary coil is charged by electronic switching which is timed such that a collapse in primary current is coupled to the secondary coil a desired number of crank angle degrees before a cylinder top dead-center position. As the secondary coil discharges, ignition energy is coupled to the appropriate spark plug. A problem with this type of system is that a failure in either of the coils, or associated charging circuitry, will totally disable the engine. Another problem is that the amount and duration of ignition energy remains fixed even though it would be desirable to increase ignition energy during starting and high engine speed or load operation.
Distributorless ignition systems are also known which have a plurality of secondary coils, each coupled across the center electrode of a pair of spark plugs. Each of the spark plug pairs is fired on both the compression stroke and exhaust stroke of the corresponding cylinders. For example, U.S. Pat. No. 4,462,380 issued to Asik discloses a distributorless ignition system having two primary coils, each magnetically coupled to a corresponding secondary coil. The outer terminals of each secondary coil are coupled to the center electrodes of a pair of spark plugs. In addition, a supplemental ignition module is disclosed for increasing the ignition energy supplied by the secondary coils. More specifically, each secondary coil has split center taps coupled to the supplemental ignition module. The supplementary ignition module includes a full wave bridge rectifier which charges an output capacitor. As the capacitor is discharged, additional energy is added to the secondary coils. Although this system addresses the Problem of increasing ignition energy, it does so by continuously supplying increased ignition energy. A disadvantage is, therefore, that the continuous increase in ignition energy adds stress to both the ignition system and spark plugs thereby decreasing their lifespan. An additional disadvantage is that a failure in any of the coils will disable a portion of the ignition energy supplied to the engine, possibly shutting down the entire engine. Another disadvantage is the complexity of the supplemental ignition module.